Desulfurization of hydrocarbon oils



Patented June 20, 1950 UNITED STAT 55 PATENT oFnc DESULFURIZATIOgflgFHYDROCABBO Albin F. Sartor, Pasadena, Tex., assignor to Shell Francisco3 Claims. (Cl. 196-24) 1 This invention relates to the catalyticdesulfurization of hydrocarbon oils by hydrogenation. More particularlythe invention relates to the desulfurization of hydrocarbon oils byhydrogenation with the aid 01 an improved catalyst which is particularlyadapted to this process.

The desulfurization of hydrocarbon oils presents a problem of 'everincreasing importance which has in the past been given considerableattention. Although various methods have been devised for the removal ofsulfur from crude petroleum and its various products, none of them areas satisfactory as would be desired. 0f the available types ofdesulfurization processes those involving the removal of sulfur byhydrogenation are the most effective and most eiiicient. These processeshave, however, the drawbacks (1) that they are relatively costly tooperate and (2) that the desulfurization is accompanied by undesiredcracking and/or hydrogenation of aromatics and/or olefins in the oilwhich not only increases the consumption of costly hydrogen, but alsoreduces the quality of the product in other respects.

In the desulfurization of hydrocarbon oils by hydrogenation it is, ofcourse, necessary that the desulfurization be eiiected with the aid of ahydrogenation catalyst. Oi the many available hydrogenation catalysts,however, only a very few are of sumcient usefulness to come intopractical consideration for this particular purpose. Although certainother catalysts have been developed which are fairly good catalysts fordesulfurization of certain types of oils, e. g. the known nickelsulfide-timgsten sulfide catalyst and the known molybdenumsulfide-cobalt sulfide-alumina. catalyst, nickel sulfide is consideredto be the most suited for the purpose because of its excellent activityand superior selectivity of action. In desulfurization by hydrogenationthe matter of selectivity of action is of prime importance not onlybecause a highly selective catalyst allows the process to be carried outmore economically, but primarily because desulfurization with a catalystof good selectivity can effect the'desired desulfurization and at thesame time improve the 2 quality of the oil in other sulfurization with acatalyst of poor selectivity can materially degrade the oil.- Forexample, in

' the desulfurization of a cracked gasoline a selective catalyst willgive a product having an octane number equal to or better than theoriginal feed, whereas a catalyst of lesser selectivitywill reduce theoctane number by several points. It is not known w t properties orcharacteristics of the catalyst uence or determine its selectivity ofaction in desulfurization. It isknown, however, that the selectivity isa property distinct from the overall activity.

For catalytic desulfurization nickel sulfide is preferably employed incombination with a relatively inert carrier or supporting material. Afairly selective catalyst for desulfurization is obtained when thenickel sulfide is combined with a diatomaceous earth. One of the bestcatalysts presently known in the art for this purpose is one preparedwith diatomaceous earth in the manner described in detail in U. '8.Patent No. 2,298,346 (which patent relates to the desu1fur ization ofhydrocarbon oils) and by Ellis, Hydrogenation of Organic Substances,page 140, sec-- tion 1141, D. Van Nostrand Company, 1930. This method ofcatalyst preparation which it will'be seen is substantially the methoddeveloped for the highly active nickel-diatomaceous earth catalyst foruse in the Fischer-Tropschprocess, involves precipitation of nickelcarbonate upon the diatomaceous-support. Catalysts prepared withdiatomaceousearth through impregnation and precipitation methodsalthough not as active as some of the above-mentioned catalysts, e. g.the tungsten sulfide nickel sulfide catalyst, molybdenum sulfide-cobaltsulfide-alumina catalyst and sulfided Raney nickel catalyst, are moreselective in their action and more active and selective than nickelsulfide catalysts prepared by other methods such as direct mixing of thesulfide and carrier.

In illustration-the characters of some of the better-known hydrogenationcatalysts in the catalytic desulfurization of hydrocarbon oils byhydrogenation are shown in the following Table I.

respects, whereas de- Table I Cetel st sumaelri ty Selectivity PbSupported upon activealumina Verypoor.-- BL- (in do Cl do (in Supportedupouactivealumlna Good-- Poor. Without carrier do D (in do Do. Supportedupon silica vel do Do.

Supported upon active alumin Poor- Fair.

dn dn" Do, Without carrier do Do. Supported upon active alumina fln p(in D0.

Supported upon alumina gel. Feir Fair. Supported upon active alumina doDo. Sulfided Raney cataly do Do. On alumina gel by impregnation -do- Do.On diatomite by pptation ex-CO: .do Do. On silica gel by impregnation doDo. Pelleted with dlatom on Do. Pigleted with diatomite by impregnadoDo.

It has now been found that the desuliurization Table H of. hydrocarbonoils by hydrogenation using a nickel sulfide catalyst may be materiallyimproved it a, catalyst is used which has been pre-- f g: gagg pared inthe particular manner now to be deg u- (03 13 scribed. This catalystcombines a good activity Liquid Hourly coupled with a good selectivity.space v lodty an The catalyst is prepared starting with preformed nickelcarbonate, 1. e. the normal car- In 55 66 bon'ate or the basiccarbonate. This material may 1 3 be obtained from any source. but it isusually 40 42 58 prepared by precipitation with or without an 0 a 3? aexcess of carbonic acid. The material may be 3 3 56 in either thehydrated or dessicated form. Comm g mercial nickel carbonate generallycontains the basic carbonate and also appreciable amounts of cobalt asan impurity. The presence of some 45 The moistened plastic mass (paste)may be cobalt in the nickel carbonate is in no way detrimental and maybe of some slight advantage.

The nickel carbonate in powdered form is mixed with a suitable amount ofa powdered, relatively inert carrier, e. g. diatomaceous earth. Theamount of nickel carbonate is adjusted such that the percentage ofnickel in the finished catalyst, on the reduced basis, lies betweenabout 25% and 75% and preferably between and 72%. The mixture is thenmoistened with an aqueous solution of ammonium hydroxide to form a thickpaste. Sufficient ammonium hydroxide should be added that the powderupon pressing in the hand forms a friable lump. 0n the other hand thepaste is preferably sufllciently thick that it does not flow or show aseparate liquid phase. A concentrated aqeuous ammonium hydroxidesolution having a gravity of at least 20 B., is preferred. In order todecrease the volatility of the ammonia the ammonium hydroxide solutionmay be partly neutralized with an acid, e. g. nitric acid, acetic acid,or hydrochloric acid, thus forming the corresponding vaporizableammonium salt.

The following table illustrates the efiect of the concentration ofnickel in nickel sulfide-diatomaceous earth catalysts under mildconditions at difierent throughput rates of oil.

extruded, for instance with a conventional auger extrusion machine, andthe extrudate may then be dried. On the other hand. the plastic mass maybe dried directly without extruding. The dried material is broken up orground to a fineness suitable for pelleting, e. g. passing a 30 meshsieve, and then formed into pellets of the desired size and shape. Aminor amount of a lubricant suchas stearic acid, graphite, aluminumflakes, starch. or the like, may be added to aid in the pelletingoperation. In some cases where pellets of considerable mechanicalstrength are not required, e. g. when the catalyst is eventually to beused in powdered form, the extruded product mentioned above may befurther treated without pellcting.

The dried pellets (or the extrudate or powder) are calcined to convertthe nickel carbonate (and/or basic nickel carbonate) to nickel oxide.The recommended calcination temperature is about 700-800 F., buttemperatures down to about 500 F. or up to about 900 F. may be used. Thecatalyst may at this point he partially'reduced by a conventionaltreatment with hydrogen at, for example, 800 F., but this step is notessential. The catalyst, whether reduced or not, is finally sulflded bytreatment with hydrogen sulfide or one of the known equivalent sulfldingagents. In effecting the sulildlng of the catalyst the temperatureshould preferably be maintained below 900 F. while temperatures as lowas about 300 F. can be applied it is preferable to maintain atemperature between about 400' F. and 800 F. The sulilding treatment ispreferably carried out only to completion since treatment with hydrogensulfide beyond this point has been found to lower the activity of thecatalyst somewhat. Thus, if the catalyst pellets are charged to thereactor and sulfided therein by a stream of hydrogen sulfide whilecontrolling the flow of hydrogen sulfide such that; the hot zone ofreaction (which moves from the inlet towards the outlet) is maintainedwithin the stated temperature range, the sulfiding is preferably stoppedas soon as appreciable amounts of hydrogen sulfide appear at the exitend of the reactor. In the sulfided catalyst the atomic ratio of nickelto sulfur is found to be somewhat above 1.32 to l which corresponds to acomposition intermediate between NiaS: and N18 or NizS. Small variationsin' this ratio do not appear to materially affect the activity of thecatalyst from which it is concluded that the detrimental effect ofovertreating is due to some other cause than the lowering of this ratio.It may be pointed out, however, that the desired ratio of at least 1.32to 1 is above that generally produced by reducing the catalyst and thenallowing it to become sulfided through use in the desulfurization of asulfur-bearing hydrocarbon oil. During use of the catalyst it is'foundthat this ratio gradually decreases and is accompanied by a paralleldecline in the activity. This decline in the activity of the catalystmay be largely prevented by operating in such a way that there is anappreciable amount of hydrogen sulfide in the hydrogen gas applied. Thiscondition may be easily maintained by recycling to the reaction zone a-Table III Approximate Percent of Temperature Original Sulfur ofSulfiding Retained in Step, F. Oil

While in the above various important details regarding the method ofpreparation are pointed out these are mainly of importance in insuringthe production of a catalyst of high activity. It is the describedmixing of the dry nickel carbonate and carrier material followed bymoistening the mixture with a small amount of aqueous ammonium hydroxide(or ammonium salt) to form a plastic mass and'the drying that isresponsible for the superior selectivity of the finished catalyst.Catalyst pellets of the same composition prepared by other methods(while observing the other important features of the preparation), suchas pelleting a mixture moistened with water. direct mixing of nickelsulfide and carrier. various impregnation methods, and the mentionedprecipitation method, may in some 6 cases have an equal activity, but donot have the selectivity of the catalyst prepared in the describedmanner.

Example Twenty-five part of diatomite (Johns-Manville grade FCdiatomaceous earth) were intimately mixed in the dry state with 117parts of nickel carbonate (NiCOa) containing 0.4% of cobalt. Afterthorough mixing, the mixture was I moistened with an aqueous solution ofammonium hydroxide (28% NHa) to form a thick plastic paste. The pastewas then dried at about 250 F. and the dried cake was broken up andground to pass a 30 mesh sieve. A small amount of stearic acid was mixedinto the powder and the mixture was formed into it inch cylindricalpellets in a conventional pelleting machine. The pellets were calcinedat '750800 F. to convert the nickel carbonate to the oxide. The calcinedpellets were then placed in a reactor and sulfided by passing acontrolled stream of hydrogen sulfide over the pellets while maintainingthe temperature at about 800 F. The resulting catalyst contained about70% nickel, calculated on the reduced basis.

A catalyst prepared in the following manner may be used for comparison.One hundred and seventeen parts of ammonium carbonate were added to 372parts of aqueous ammonium hydroxide (28%). One hundred and seventeenparts of the above-mentioned nickel carbonate was added; This solutionwas then used to impregnate 25 parts of the above-mentioned diatomaceousearth. After drying at about 250 F. and grinding the material to pass a30- mesh sieve, the catalyst was completed as described above. Thefinished catalyst contained about 70% nickel on the reduced basis. 1

The above catalysts were used in the desulfurization of a Dubbs pressuredistillate gasoline of about 370-400 F. end point having the following 7inspection data.

Bromine number Sulfur, per cent by weight 0.363 Maleic anhydride value30 Octane number, clear 70.2

The conditions of operation were substantially identical and were asfollows:

First Comparison Catalyst Catalyst Temperature, F 602 508 Pressure, p.s. i. g 75 75 Liquid hourly space velocity. 8. 0 8. 3 Mol ratio, rnoin... l. 74 2. 00

The results obtained in the two cases are shown It will be seen that thecatalyst prepared in the described manner removed 44% of the originalsulfur, reduced the maleic anhydride value to l and increased the clearoctane number by 1.5 points without hydrogenating the olefins, eventhough the space velocity wasvery high.(8.0) and the pressure was verylow (75 p. s. i. g.). While under the conditions employed in the givenexample the reduction in the concentration of sulfur was only 44% it ispossible to remove up to at least 92% of the sulfur with only a nominalhydrogenation, e, g. 17%, of the olefins by the use of a lowerthroughput rate. The ability of the catalyst to hydrogenate sulfurcompounds more or less selectively is increased. rather than decreased,by operating at low space velocities.

The comparison catalyst having the same composition and prepared by anaccepted method removed only 3196 of the sulfur, reduced the maleicanhydride value to only and increased the clear octane number by only0.5 point. If the severity of the conditions were increased using thesec- 0nd catalyst in order to obtain the same degree of removal ofsulfur and reduction in maleic anhydride value an appreciable amount ofthe olefins would be hydrogenated and the clear octane number would bereduced.

It is to be noted that the comparison catalyst is one having a fairactivity and a fairly good selectivity as indicated in the aboveTable 1. Thus, for comparison a cobalt sulfide-molybdenumsulfide-alumina catalyst frequently recommended for use in catalyticdesulfurization gave the following results when treating a very similarpressure distillate gasoline from the same source under the sameconditions.

Per cent oleflns retained 84 Per cent sulfur retained 50 Maleicanhydride value of product 1 Change in clear octane number 2.5

Upon inspection of Table I it may be noticed that the hydrogenationcatalysts having\ the highest activity (designated as good) have a poorselectivity whereas some of the catalysts having a poor activity have afairly good selectivity. This relationship, however, holds only in avery general way since, as can be seen in the above example, somecatalysts are more active as well as more selective than others. Theactivity as this term is herein used refers to the ability of thecatalyst to catalyze the hydrogenation of the sulfur compounds in theoil and not to the activity of the catalyst in catalyzing hydrogenationof olefins or other compounds.

While in the above attention has been focused primarily on a nickelsulfide catalyst prepared with diatomaceous earth, this is because thisparticular carrier has been found to give catalysts which are for someunknown reason somewhat superior to other common carrier materials.Other relatively inert carrier materials such as the aluminas, silicagels, magnesia, certain clays and the like do however give catalystswhich are sufllciently good to be applied commercially and theselikewise may be improved by preparing them in the manner described. Thedescribed and claimed method of preparation is for this reason not to beconsidered limited to the preparation of nickel sulfide catalysts withdiatomaceous earth.

In the catalytic desulfurization of hydrocarbon oils using a catalystprepared as just described the oil to be desulfurized is contacted withthe catalyst in the presence of hydrogen or a gas consistingpredominantly of hydrogen at a temperature in the order of 450 to 850 F.The oil to be desulfurized may be in the vapor phase, liquid phase, ormixed phase. The pressure is preferably at least 75 pounds per squareinch (gage) and preferably above 150 pounds per square inch. In generalthe desulfurization and maintenance of the catalytic activity areimproved with increasing pressure. In practice, however, thisimprovement must be weighed against the much greater plant costs foroperation at higher pressures. An additional advantages of the describedcatalyst is that it allows the desulfurization to be carried out quitesatisfactorily at pressures considerably lower than those generallyconsidered practicable with the previously known catalysts. Thus, aspointed out, the desuli'urization may be carried out at pressures below200 pounds per square inch and even below 100 pounds per square inch.The rate of throughput of the oil may vary from about 0.3 up to about 16volumes of oil per volume of catalyst bed per hour and is preferablyadjusted for each individual case to effect the desired degree ofdesulfurization.

When desulfurizing lower boiling hydrocarbon oils such as olefiniccracked gasolines and fractions thereof boiling below about 500 IF. itis usually desired to operate with the oil in the vapor phase, and whendesulfurizing higher boiling oils such as cracked gas oils and the likeit isv usually preferable to operate with the oil at least partly in theliquid phase. One particularly suitable method which is applicable bothwith lower and higher boiling oils is to trickle the liquid oil downover a bed of the catalyst countercurrent to a small stream of thehydrogen gas. When desulfurizing very heavy or dirty oils a particularlysuitable method is to dilute the oil with suflicient lower boilingnapthenic hydrocarbons to lower the critical temperature of the mixtureto within the preferred temperature range and then to work with verysmall amount of hydrogen under a pressure above the critical pressure ofthe mixture. The high solvent power of the dense pseudo liquid phase inthis method of operation prevents contamination of the catalyst withtarry deposits which otherwise tend to form when treating oils of thischaracter.

I claim as my invention:

1. in a process for the removal of sulfur from a sulfur-bearinghydrocarbon oil by catalytic hydrogenation with a nickel sulfidecatalyst, the

improvement which comprises contacting the oil to be desulfurized underhydrogenation conditions with a nickel sulfide catalyst which has beenprepared by mixing nickel carbonate with powdered relatively inertcarrier material, adding aqueous ammonium hydroxide to form the mix tureinto a paste, drying, calcining, and sulflding.

2. In the removal of sulfur from a sulfur-bearing hydrocarbon oil bycatalytic hydrogenation 3. A process for the removal of sulfur from a Isulfur-bearing hydrocarbon oil which comprises contacting the oil to bedesulfurized with a hydrogen under hydrogenation conditions with anickel sulfide-diatomaceous earth catalyst prepared by mixing performednickel carbonate with diatomaceous earth in the dry state, forming themixture into a paste by the addition of an aqueous solution 01 ammoniumhydroxide, drying, calcin- REFERENCES CITED The following references areof record in the tile 01 this Patent:

10 UNITED STATES PATENTS Number I Name Date Arnold May 8, 1923Muhlenberg Mar. 11, 1930 Gaus et a1 Oct. 24; 1933 Rosenstein Sept. 25,1934 Szeyna Feb. 17, 1942 Corson et a1 Oct. 13, 1942

1. IN A PROCESS FOR THE REMOVAL OF SULFUR FROM A SULFUR-BEARING HYDROCARBON OIL BY CATALYTIC HYDROGENATION WITH A NICKEL SULFIDE CATALYST, THE IMPROVEMENT WHICH COMPRISES CONTACTING THE OIL TO BE DESULFURIZED UNDER HYDROGENATION CONDITIONS WITH A NICKEL SULFIDE CATALYST WHICH HAS BEEN PREPARED BY MIXING NICKEL CARBONATE WITH POWERED RELATIVELY INERT CARRIER MATERIAL, ADDING AQUEOUS AMMONIUM HYDROXIDE TO FORM THE MIXTURE INTO A PASTE, DRYING, CALCINING, AND SULFIDING. 